Liquid crystal display device equipped with an improved backlight device

ABSTRACT

A liquid crystal display device irradiates a light of a light source from a backside of a liquid crystal panel. A light-guiding plate provided under the liquid crystal panel guides the light of the light source to the liquid crystal panel by transmitting the light therethrough. An optical sheet is arranged between the liquid crystal panel and the light-guiding plate. A backlight housing accommodates the light-guiding plate and the optical sheet. The optical sheet has a protruding part extending outwardly from a periphery thereof. The backlight housing has an opening at a position corresponding to the protruding part.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to liquid crystal displaydevices and, more particularly, to a liquid crystal display deviceequipped with a backlight device that illuminates a liquid display part.

2. Description of the Related Art

First, a description will be given, with reference to FIG. 1, of aconventional liquid crystal display device. FIG. 1 is an explodedperspective view of a conventional liquid crystal display device.

A liquid crystal panel 1 of the liquid crystal display device, whichdisplays information thereon, is accommodated in a housing 2 that alsoserves as a decorative board. A backlight device is provided under theliquid crystal panel 1 so as to make the liquid crystal display legibleby illuminating from backside.

The backlight device has light sources 3, a light-guiding plate 4 andoptical sheets 5 a and 5 b. The light sources 3, the light-guiding plate4 and the optical sheets 5 a and 5 b are accommodated in a backlighthousing comprising upper and lower housings 6 a and 6 b.

A light emitted from each of the light sources 3 propagates inside thelight-guiding plate 4, and exits from a front surface of thelight-guiding plate 4 toward the liquid crystal panel 1. A reflectivepanel 7 is provided on a side of the light-guiding plate 4 opposite tothe light-guiding plate 4, and the light projected from each of thelight sources 3 and incident on the light-guiding plate 4 exits only ina direction toward the liquid crystal panel 1.

The light that exits from the light-guiding plate 4 is irradiated ontothe liquid crystal panel 1 after being subjected to a predeterminedoptical process such as diffusion or convergence by the optical sheets 5a and 5 b. Thereby, the background of the liquid crystal panel 1 becomesbright moderately, which makes the display on the liquid crystal panel 1legible.

Although the two optical sheets 5 a and 5 b are used in the device shownin FIG. 1, a single optical sheet may be used if a desired backlighteffect can be obtained, or there may be a case where more than threeoptical sheets are used. Additionally, although the two light sources 3are provided on opposite sides of the light-guiding plate 4 in FIG. 1,only one light source may be provided on one side.

In the structure of the backlight device shown in FIG. 1, each of theoptical sheets 5 a and 5 b has the front surface and the back surface,and does not function correctly if it is mistakenly incorporated in awrong direction. Therefore, it is necessary to check, after assemblingthe backlight device, whether the optical sheets 5 a and 5 b have beenincorporated and whether their front and back surfaces face correctly.

However, after assembling the backlight device, the optical sheets 5 aand 5 b are covered by the liquid crystal panel 1 and the backlighthousing 6 a. Therefore, there is a problem in that it is difficult tocheck visually from outside, after the assembly of the backlight device,whether the optical sheets 5 a and 5 b are appropriately incorporated.

Here, if an ambient temperature of the liquid crystal display device israised in an environmental test etc., the optical sheets 5 a and 5 bwill expand thermally. Under such circumstances, there is a case inwhich a periphery of each of the optical sheets 5 a and 5 b shiftstoward the center thereof without extending outwardly. In such a case,each of the optical sheets 5 a and 5 b deforms into a fine-wavy form asshown in FIG. 2B.

That is, if the gap between the backlight housing 6 b and thelight-guiding plate 4 is large, each of the optical sheets 5 a and 5 bmakes a smooth deformation in which a center section protrudes as shownin FIG. 2A. However, if the gap is small as shown in FIG. 2B, each ofthe optical sheets 5 a and 5 b will deform into the wavy form havingmany fine waves. If the optical sheets 5 a and 5 b deform as shown inFIG. 2B, there is a problem in that a light passing through the opticalsheets 5 a and 5 b is influenced and unevenness occurs in the backlightillumination.

Moreover, although a light-guiding plate 4 also expands in connectionwith the temperature rise, the light-guiding plate 4 deforms so that thecenter portion thereof is bent since the periphery thereof is fixed andthe thickness thereof is larger than the thickness of the optical sheetand the light-guiding plate 4 has rigidity. Here, when the centerportion of the light-guiding plate 4 bends in a direction to separatefrom the liquid crystal panel 1, the gap between the liquid crystalpanel 1 (the upper backlight housing 6 b) and the light-guiding plate 4expands only in the center portion. Therefore, the space within whichthe optical sheets 5 a and 5 b can deform is expanded, and there is aproblem in that a magnitude of deformation further increases.

Each of the light sources 3 shown in FIG. 1 consists of a fluorescencetube, which generally uses an ultraviolet radiation of mercury. FIG. 3is a perspective view of the light source 3 that consists of afluorescence tube. In the light source 3, opposite ends of afluorescence tube 3 a is attached to fluorescence tube support members 3b, and a reflector 3 c is provided around the fluorescence tube 3 a. Thereflector 3 c has a function to reflect a light emitted from thefluorescence tube 3 a and converge the reflected light onto an incidentlight end surface of the light-guiding plate 4. The fluorescence tube 3a also emits heat when emitting a light. Such a heat is released throughthe reflector 3 c and the fluorescence tube support members 3 b.

As mentioned above, since an ultraviolet radiation of mercury is usedfor the fluorescence tubing 3 c, mercury vapor is enclosed within aglass tube, which constitutes the luminescence portion. Here, if awall-surface temperature of the glass tube changes, a mercury vaporpressure inside the glass tube changes, which results in a change in theluminous efficiency. Such a change in the luminous efficiency takes apeak value (maximum) at a certain temperature if the glass wall surface.Therefore, in order to maintain a high luminous efficiency, it isnecessary to maintain the wall surface of glass tube at a constanttemperature.

Moreover, a cold cathode tube can also be used for the fluorescencetube. In such a case, when a cold cathode tube emits electrons, muchelectric power (=cathode drop voltage×tube current) near the cathode.Such an electric power is reflected to as a reactive power, and mostparts of the reactive power are converted into heat. If the liquidcrystal display device is enlarged and the intensity of luminescence ofthe backlight is raised, a cathode drop electrical potential differenceand a tube current, which are the main components of a tubing electricalpotential difference, will go up inevitably. Consequently, generation ofheat of the fluorescence tube end section, which is the cathode section,will become larger relative to other part.

As mentioned above, generation of heat of the fluorescence tube-endportion, which is the cathode section, increases, the temperature nearthe fluorescence tube-end portion rises and creep may occur in a solderconnecting a terminal and a lead wire. If creep occurs in a solder, itcauses a poor connection, and there is a problem in that a reliabilityof dependability of a connection falls remarkably. Generally, a creepphenomenon starts to occur at 0.5 times the melting point of thematerial. Usually, since the melting point of a solder is 183° C., ahalf of the melting point is 91.5° C. It is appreciated from theexperiments that if the temperature of the solder exceeds 100° C., thecreep appears remarkably.

Moreover, when the temperature near the fluorescence tube-end portionrises, there is a problem in that heat deformation and thermaldegradation occur in a resin member such as the light-guiding plate 4 ora plastic frame, which are members arranged around the fluorescencetube. In order to solve the problem caused by the generation of heat insuch a fluorescence tube and to maintain the luminous efficiency at ahigh value, it is necessary to properly control a heat radiation fromthe fluorescence tube.

However, in the structure of the conventional light source 3, a heat isradiated from only the by reflector 3 c which merely encloses thefluorescence tube 3 a and the fluorescence tube support member, and thetemperature control of the fluorescence tube and a peripheral portionthereof according to the heat radiation is not taken into consideration.Therefore, there is a problem in that the luminous efficiency of thefluorescence tube cannot be maintained in a good state.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedand useful liquid crystal display device in which the above-mentionedproblems are eliminated.

A more specific object of the present invention is to provide a liquidcrystal display device having a backlight device including an opticalsheet of which existence can be visually recognized from outside.

Another object of the present invention is to provide a liquid crystaldisplay device having a backlight device including an optical sheet thatis prevented from deformation due to thermal expansion.

A further object of the present invention is to provide a liquid crystaldisplay device having a backlight device that can eliminate a problemcaused by a heat of a light source.

In order to achieve the above-mentioned objects, there is providedaccording to one aspect of the present invention a liquid crystaldisplay device irradiating a light of a light source from a backside ofa liquid crystal panel, the liquid crystal display device comprising:the liquid crystal panel; a light-guiding plate provided under theliquid crystal panel for guiding the light of the light source to theliquid crystal panel by transmitting the light therethrough; at leastone optical sheet arranged between the liquid crystal panel and thelight-guiding plate; and a backlight housing accommodating thelight-guiding plate and the optical sheet, wherein the optical sheet hasa protruding part extending outwardly from a periphery thereof, and thebacklight housing has an opening at a position corresponding to theprotruding part.

According to the above-mentioned invention, present, the openingprovided in the backlight housing serves as a housing window throughwhich the protruding part of the optical sheet can be visuallyrecognized after the liquid crystal display device is assembled. Thus, adefect in the liquid crystal display device, such as a fact that theoptical sheet are forgotten to insert during an assembling operation,can be easily checked.

In the liquid crystal display device according to the present invention,a plurality of the optical sheets may be provided, and the protrudingparts of the optical sheets may be located at different positions fromeach other. Accordingly, the protruding parts do not overlap with eachother, and presence of all optical sheets can be checked visually. Theprotruding part may be provided at a position other than positions alonga center line of the optical sheet. Accordingly, if the optical sheet isplaced upside down, the protruding part cannot be aligned with thewindow of the housing. Thus, the fact that the optical sheet isassembled upside down can be checked visually.

Additionally, there is provided according to another aspect of thepresent invention a liquid crystal display device irradiating a light ofa light source from a backside of a liquid crystal panel, the liquidcrystal display device comprising: the liquid crystal panel; alight-guiding plate provided under the liquid crystal panel for guidingthe light of the light source to the liquid crystal panel bytransmitting the light therethrough; at least one optical sheet arrangedbetween the liquid crystal panel and the light-guiding plate; and abacklight housing accommodating the light-guiding plate and the opticalsheet, wherein the optical sheet is located within a gap formed betweenthe backlight housing and the light-guiding plate, and a width of thegap at the center of the optical sheet is smaller than a width of thegap at an end of the optical sheet.

According to the above-mentioned invention, when the optical sheetexpands thermally, the deformation of the optical sheet does notconcentrate into the center portion since there is no space in which thedeformation occurs. Thus, the optical sheet deforms along a relativelygentle curve, which prevents uneven illumination by the light passingthrough the optical sheet.

In the liquid crystal display device according to the above-mentionedinvention, the backlight housing may have a protruding part formed inthe middle of a surface facing the light-guiding plate, and a width ofthe gap at the center of the optical sheet may be equal to a distancebetween the protruding part and the light-guiding plate. Accordingly,dimensions of the space in which the optical sheet is placed can beeasily set by forming the protruding part on the backlight housing. Theprotruding part may have a length equal to one fourth of a length of theoptical sheet. Accordingly, the optical sheet tends to deform along theprotruding part, which prevents generation of small waveform deformationin the optical sheet.

Additionally, there is provided according another aspect of the presentinvention a liquid crystal display device using a light of a lightsource as a backlight, the liquid crystal display device comprising: aliquid crystal panel; and a light-guiding plate provided under theliquid crystal panel for guiding the light of the light source to theliquid crystal panel by transmitting the light therethrough, wherein thelight source includes a fluorescent tube and a reflector surrounding thefluorescent tube, and a configuration of a portion of the reflectorsurrounding a luminescence section of the fluorescent tube is differentfrom a configuration of has a portion of the reflector surrounding anelectrode section of the fluorescent tube.

According to the above-mentioned invention, different heat releasecharacteristics can be provided to the portion of the reflectorsurrounding the luminescence section of the fluorescent tube and theportion of the reflector surrounding the electrode section of thefluorescent tube. Accordingly, the temperature of the fluorescent tubecan be accurately adjusted, and the luminescence characteristic of theluminescent tube can be maintained at a high level.

In the liquid crystal display device according to the above-mentionedinvention, a step part may be formed between the portion of thereflector surrounding the luminescence section of the fluorescent tubeand the portion of the reflector surrounding the electrode section ofthe fluorescent tube, and a distance between the electrode section ofthe fluorescent tube and the reflector may be smaller than a distancebetween the luminescence section of the fluorescent tube and thereflector. Accordingly, an amount of heat released form the electrodesection of the fluorescent tube can be larger than an amount of heatreleased from the luminescence section, which results in decrease in thetemperature of the electrode section. Thus, the solder connecting partprovided in the electrode section can be prevented from being affectedby a high temperature.

In the liquid crystal display device according to the above-mentionedinvention, the electrode section of the fluorescent tube may preferablybe connected to a fluorescent tube support part having a heatconductivity equal to or greater than 0.5 [W/(m·K)]. The reflector maybe made of a metal or a material having a heat conductivitysubstantially equal to a heat conductivity of a metal. Accordingly, anamount of heat released from the reflector is increased, which resultsin decrease in the temperature of the fluorescent tube.

Other objects, features and advantages of the present invention willbecome more apparent from the following detailed description when readin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded view of a conventional liquid crystal displaydevice;

FIGS. 2A and 2B are illustrations of an optical sheet for explaining amode of deformation;

FIG. 3 is a perspective view of a light source comprising fluorescencetubes;

FIG. 4A is an exploded perspective view of a liquid crystal displaydevice according to a first embodiment of the present invention;

FIG. 4B is an exploded view of a part of a backlight housing shown inFIG. 4A;

FIG. 5 is a cross-sectional view of a liquid crystal display deviceaccording to a second embodiment of the present invention;

FIG. 6 is an enlarged view of a part indicated by a dotted circle A ofFIG. 5;

FIG. 7 is an enlarged view of a part indicated by a doted circle B ofFIG. 5;

FIG. 8 is an illustration showing a protruding part;

FIG. 9 is a cross-sectional view of a liquid crystal display deviceaccording to a variation of the liquid crystal display device shown inFIG. 5;

FIG. 10 is a cross-sectional view of a liquid crystal display deviceaccording to another variation of the liquid crystal display deviceshown in FIG. 5;

FIG. 11 is a perspective view of a light source provided in a liquidcrystal display device according to a third embodiment of the presentinvention;

FIG. 12 is a perspective view of the light source shown in FIG. 11;

FIG. 13 is a cross-sectional view of a part corresponding to a peripheryof a glass tube heat-emitting section of a reflector;

FIG. 14 is a cross-sectional view of a part corresponding to a peripheryof a fluorescent tube support member of the reflector; and

FIG. 15 is a cross-sectional view of the reflector.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will now be given, with reference to FIGS. 4A and 4B, of afirst embodiment of the present invention. FIG. 4A is an explodedperspective view of a liquid crystal display device according to thefirst embodiment of the present invention. FIG. 4B is a plan view of apart of a backlight housing shown in FIG. 4A. In FIGS. 4A and 4B, partsthat are the same as the parts shown in FIG. 1 are given the samereference numerals, and descriptions thereof will be omitted.

Although the liquid crystal display device according to the firstembodiment of the present invention has the same basic structure as theliquid crystal display device shown in FIG. 1, a configuration ofoptical sheets and a lower backlight housing are different. That is, inthe backlight device of the liquid crystal display device according tothe present embodiment, as shown in FIG. 4A, optical sheets 10 a and 10b is provided with protruding parts 10 a-1 and 10 b-1, respectively, andthe lower backlight housing 12 is provided with a housing aperture 12 a.

A housing 2 as a decorative panel is formed in the shape of a box by ametal plate, such as a stainless steel plate, an iron plate or analuminum plate, and has a function to reinforce a liquid crystal panel 1accommodated in the housing 2. The optical sheets 10 a and 10 b areprovided under the liquid crystal panel 1, and a light-guiding plate 4is provided under the optical sheets 10 a and 10 b. The light-guidingplate 4 is formed of a highly transparent resin such as acrylic resin,and has a function to lead a light from a light source 3 to the liquidcrystal panel 1. The optical sheets 10 a and 10 b are thin sheets whichapply optical processing such as divergence or convergence to the lightled to the liquid crystal panel 1.

The light source 3, which consists of a fluorescence tube, is arrangedon each side of the light-guiding plate 4 so as to project a lighttoward a light incidence end surface of the light-guiding plate 4. Thelight emitted from the light source 3 in a direction opposite to theliquid crystal panel 1 is reflected by a reflecting plate 7. Thereby,the great portion of the light incident on the light-guiding plate 4exits toward the liquid crystal panel 1.

The optical sheets 10 a and 10 b, the light-guiding plate 4, thereflecting plate 7 and the light source 3 are accommodated between anupper backlight housing 6 a and a lower backlight housing 12, therebyconstituting a backlight device. The upper backlight housing 6 a and thelower backlight housing 12 are formed as a resin mold component such aspolycarbonate, or formed of a metal plate such as a stainless steelplate, an iron plate or an aluminum plate. The backlight device isattached to a housing 2 so as to be located under the liquid crystalpanel 1.

The optical sheets 10 a and 10 b provided with the protruding parts 10a-1 and 10 b-1 are arranged, when assembled as a backlight device, in aposition corresponding to a housing aperture 12 a of the backlighthousing 12. That is, the housing aperture 12 a is an opening provided inthe backlight housing 12, and is configured so that the protruding parts10 a-1 and 10 b-1 can be visually recognized from outside through thehousing aperture 12 a. Therefore, it can be inspected whether theoptical sheets 10 a and 10 b are incorporated by checking whether theprotruding parts 10 a-1 and 10 b-1 exist in the housing aperture 12 aafter the assembly of the liquid crystal display device.

In the above-mentioned structure, although the two optical sheets 10 aand 10 b are provided, if the protruding parts 10 a-1 and 10 b-1 arelocated in a completely overlapping position, the protruding part 10 a-1is covered by the protruding part 10 b-1, which causes difficulty in thevisual check of the optical sheets. In such a case, existence of the twooptical sheets 10 a and 10 b can be easily checked by providing theprotruding parts 10 a-1 and 10 b-1 in different positions so as to notoverlap with each other. Thereby, when the liquid crystal display deviceis assembled without incorporating both or one of the optical sheets 10a and 10 b, it can be easily recognized by a visual inspection, and thequality of the liquid crystal display device is prevented from fallingdue to both or one of the optical sheets not having been incorporated.

Moreover, it can also be checked easily whether or not the opticalsheets 10 a and 10 b are incorporated with the front and back surfacesin a proper state by providing the protruding parts 10 a-1 and 10 b-1 inan asymmetrical position with respect to a center line of the opticalsheets 10 a and 10 b. That is, by providing the protruding parts 10 a-1and 10 b-1 in the asymmetrical position which is offset from the centerline of the optical sheets 10 a and 10 b, when the optical sheets 10 a-1and 10 b-1 are incorporated upside down, the position of the protrudingparts 10 a-1 and 10 b-1 is on the opposite side with respect to thecenter line, which causes the protruding parts 10 a-1 and 10 b-1disappear from the housing aperture 12 a. Therefore, it can be easilychecked by a visual inspection whether or not the optical sheets 10 aand 10 b are assembled with the front and back surfaces being correctlypositioned, and the quality of the liquid crystal display device isprevented from falling due to the optical sheets 10 a and 10 b havingbeen incorporated with upside down.

A description will now be given, with reference to FIG. 5, of a secondembodiment of the present invention. FIG. 5 is a cross-sectional view ofthe liquid crystal display device by the second embodiment of thepresent invention. In FIG. 5, parts that are the same as the parts shownin FIG. 4 are given the same reference numerals, and descriptionsthereof will be omitted.

As shown in FIG. 5, the liquid crystal display device according to thepresent embodiment has the same structure as the liquid crystal displaydevice shown in FIG. 4 except for the difference regarding theconfiguration of an upper backlight housing 20. That is, the upperbacklight housing 20 shown in FIG. 5 is constituted by a resin frame,and a protruding part 20 a is formed on a surface of the housing 20which faces the optical sheet 10 a. The protruding part 20 a is formedin a center portion of the backlight housing 20 in FIG. 5, and is formedso as to protrude toward the optical sheet 10 a. For example, if a totalthickness of the two optical sheets 10 a and 10 b is 0.58 mm, a distancebetween the center portion of the protruding part 20 a and thelight-guiding plates 4 is set to be 0.6 mm, while a distance between thebacklight housing 20 and the light-guiding plate 4 is set to be 0.7 mmin portions other than the protruding part 20 a. Here, the distancebetween the center portion of the protruding part 20 a and thelight-guiding plates 4 and the distance between the backlight housing 20and the light-guiding plate 4 correspond to gaps in which the opticalsheets 10 a and 10 b are arranged.

FIG. 6 is an enlarged view of a part indicated by a dotted circle A ofFIG. 5, and FIG. 7 is an enlarged view of a part indicated by a dotedcircle B of FIG. 5. As shown in FIG. 6, the protruding part 20 a of thecenter portion of the upper backlight housing 20 formed by a resin frameis arranged in a state where there is almost no gap between theprotruding part 20 a and the optical sheets 10 a and 10 b arranged onthe light-guiding plate 4. On the other hand, as shown in FIG. 7, in theend part of the optical sheet, a predetermined gap is formed between theback surface of the backlight housing 20 and the optical sheet 10 a.

FIG. 8 is an illustration showing the configuration of the protrudingpart 20 a. As shown in FIG. 8, the protruding part 20 a is formed in around shape such as, for example, an arc of a large radius. It ispreferable that the length of a part in which the protruding part 20 ais formed is about ¼ of the length of the optical sheet.

In the above structure, when the optical sheet expands thermally, thereis no space in which a bent portion is formed since the center portionis provided with the protruding part 20 a. For this reason, generationof bending will be concentrated and toward the end of the optical sheet.

Here, since the protruding part 20 a is formed with a smooth roundness,the optical sheet will bend in accordance with the configuration of theprotruding part 20 a, and bending of fine waves as shown in FIG. 2Bhardly occurs. Therefore, generation of unevenness in the brightness dueto fine waves of the optical sheet can be prevented.

FIG. 9 is a cross-sectional view of a liquid crystal display device,which is a variation of the liquid crystal display device shown in FIG.5. In the liquid crystal display device shown in FIG. 9, the lightsource 3 is provided on only one side of the light-guiding plate 4. Thebacklight housing 20 is provided with the protruding part 20 a similarto the liquid crystal display device shown in FIG. 5.

FIG. 10 is a cross-sectional view of a liquid crystal display device,which is another variation of the liquid crystal display device shown inFIG. 5. The liquid crystal display device shown in FIG. 10 has asmoothly bent surface on which the optical sheet of the light-guidingplate 4 is arranged in the liquid crystal display device shown in FIG. 9instead of providing the protruding part 20 a. Also according to such astructure, an effect similar to the case in which the protruding part 20a is provided can be obtained.

A description will now be given of a third embodiment of the presentinvention.

First, a description will be given of a mode of heat radiation from afluorescent tube is explained.

Generally, heat moves from a body to other bodies according to threekinds of forms, heat conduction, heat transfer and heat radiation. Inthe backlight device of a side light system as shown in FIG. 1, theluminescence section of the fluorescent tube is arranged in the closednarrow space between the reflector and the light-guiding plate. For thisreason, there are few amounts of movements of the heat according toconvection of air around the luminescence section.

Moreover, since the emissivity of the inner surface of the reflector isclose to 1, the reflector hardly absorbs radiation heat. Therefore, alarge part of the heat emitted from the fluorescent tube reaches thereflector according to heat conduction in the air layer surrounding thefluorescent tube. Further, the electrode section of the fluorescent tubeis surrounded by the fluorescent tube support section, and the heatgenerated in the electrode section of the fluorescent tube reaches thereflector according to heat conduction through the fluorescent tubesupport section.

As mentioned above, a large part of heat from the fluorescent tube istransmitted to the reflector according to heat conduction, and isemitted further to outside from the reflector. Here, an amount Q [W] ofheat, which moves according to heat conduction, can be expressed by thefollowing equation.Q=λ/δ(Ti−To)A[W]In the above equation, λ represents a thermal conductivity [W/(m·K)] ofa medium through which heat moves, δ represents a thickness [m] of themedium, Ti and To express a wall-surface temperature [K] of the medium,and A represents a cross-sectional area [m²] of the medium.

When surrounded by an air layer like the luminescence section of thefluorescent tube, an amount of heat release, that is, an amount Q oftransfer of heat can be adjusted by adjusting the thickness δ of the airlayer since the thermal conductivity of air is almost constant, 0.026[W/(m·K)]. Namely, what is necessary is to adjust a distance between theluminescence section of the fluorescent tube and the reflector.Moreover, an amount of heat released from the electrode section can beadjusted by adjusting a thickness of the fluorescent tube supportmember.

Therefore, in order to adjust the amount of heat release by both theluminescence section and the electrode section of the fluorescent tube,it is necessary to adjust independently both the distance between theinner surface of the reflector and the luminescence section of thefluorescent tube and the distance between the inner surface of thereflector and the electrode section of the fluorescent tube. Such anadjustment can be achieved by providing a step to the reflector.

FIG. 11 is a perspective view of the light source provided in the liquidcrystal display device according to the third embodiment of the presentinvention. The light source 40 shown in FIG. 11 is provided instead ofthe light source 3 shown in FIG. 3.

In the light source 3 shown in FIG. 3, the reflector 3 c has a uniformcross-sectional configuration, and is provided around the fluorescencetube 3 a and the fluorescent tube support members 3 b. On the otherhand, in the light source 40 shown in FIG. 11, the cross-sectionalconfiguration of a reflector 46 differs between a portion surroundingfluorescent tubes 42 and a portion surrounding fluorescent tube supportmembers 44.

FIG. 12 is an exploded perspective view of the light source 40. A steppart 46 a is formed in the vicinity of each end of the reflector 46 sothat the fluorescent tube support member 44 is provided to a portionbetween the step part 46 a and the end of the reflector 46. Therefore,the fluorescent tubes 42 are provided in a portion between the oppositestep parts 46 a of the reflector 46.

In the light source 40 having the reflector 46 of the above structure,heat emitted from a glass tube heat-emitting section (luminescencesection) 42 a of the fluorescent tube 42 reaches the reflector 46through the air layer around the fluorescent tube 42, and is furtherreleased outside from the reflector 46. On the other hand, heat emittedfrom the electrode section 42 b of the fluorescent tube 42 reaches thereflector 46 through the fluorescent tube support member 44, and isfurther released outside from the reflector 46.

As mentioned above, the step part 46 a is provided between the portionof the reflector 46 surrounding the glass tube heat-emitting section 42a and the portion of the reflector 46 surrounding the fluorescent tubesupport member 44. Thereby, the distance between the inner surface ofthe reflector 46 and the fluorescent tube 42 are varied.

FIG. 13 is a cross-sectional view of the portion of the reflector whichportion surrounds the glass tube heat-emitting part 42 a. FIG. 14 is across-sectional view of the reflector 46 which portion surrounds thefluorescent tube support member 44. The distance between the innersurface of the reflector 46 and the fluorescent tube 42 is indicated byD1 in FIG. 13 and D2 in FIG. 14. Adjustment of the distances D1 and D2is made by changing a length L of an opening and a radius R of curvatureof a bent portion of the reflector 46 as shown in FIG. 15.

In the fluorescent tube, since an amount of heat generated in theelectrode section is larger than an amount of heat generated in theluminescence section, the distance D2 shown in FIG. 14 is set smallerthan the distance D1 shown in FIG. 13. That is, it is constituted sothat an amount of heat released from the electrode section 42 b of thefluorescent tube 42 is larger than an amount of heat released from theluminescence section 42 a.

Moreover, the fluorescent tube support member 44 is preferably made ofan insulating material having a high thermal conductivity equal to ormore than 0.5 [W/(m·K)] so as to increase the heat release efficiency.As for such an insulating material, a commercially available siliconesealant having a high heat conductivity, for example, 1.59 [W/(m·K)] maybe used.

Moreover, in order to increase a heat release efficiency of thereflector 46, the reflector is preferably made of metal or a materialhaving a heat conductivity equivalent to metal.

As mentioned above, the temperature of the fluorescent tube can beadjusted with high accuracy by adjusting an amount of heat release basedon the amount of heat release which varies between portions of thefluorescent tube. Thus, the temperature of the luminescence section ofthe luminescent tube can be adjusted to maintain a temperature at whichthe maximum luminescence efficiency is obtained.

Moreover, since the temperature of the electrode section can be loweredby increasing an amount of heat released from the electrode section offluorescent tube, the temperature of a solder connecting part providedto the fluorescent tube support member can also be lowered, therebyimproving the reliability of the solder connecting part. Furthermore,the light-guiding plate and the plastic frame arranged around thefluorescent tube are prevented from thermal deformation and thermaldegradation.

The present invention is not limited to the specifically disclosedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

The present application is based on Japanese priority application No.2001-236400 filed on Aug. 3, 2001, the entire contents of which arehereby incorporated by reference.

1. A liquid crystal display device irradiating a light of a light sourcefrom a backside of a liquid crystal panel, the liquid crystal displaydevice comprising: the liquid crystal panel; a light-guiding plateprovided under said liquid crystal panel for guiding the light of saidlight source to said liquid crystal panel by transmitting the lighttherethrough; at least one optical sheet arranged between said liquidcrystal panel and said light-guiding plate; and a backlight housingaccommodating said light-guiding plate and said optical sheet, whereinsaid optical sheet has a protruding part extending outwardly from aperiphery thereof, and said backlight housing has an opening at aposition corresponding to said protruding part.
 2. The liquid crystaldisplay device as claimed in claim 1, wherein a plurality of saidoptical sheets are provided, and said protruding parts of said opticalsheets are located at different positions from each other.
 3. The liquidcrystal display device as claimed in claim 1, wherein said protrudingpart is provided at a position other than positions along a center lineof said optical sheet. 4-6. (canceled)
 7. A liquid crystal displaydevice using a light of a light source as a backlight, the liquidcrystal display device comprising: a liquid crystal panel; and alight-guiding plate provided under said liquid crystal panel for guidingthe light of said light source to said liquid crystal panel bytransmitting the light therethrough, wherein said light source includesa fluorescent tube and a reflector surrounding said fluorescent tube,and a configuration of a portion of said reflector surrounding aluminescence section of said fluorescent tube is different from aconfiguration of has a portion of said reflector surrounding anelectrode section of said fluorescent tube.
 8. The liquid crystaldisplay device as claimed in claim 7, wherein a step part is formedbetween said portion of said reflector surrounding said luminescencesection of said fluorescent tube and said portion of said reflectorsurrounding said electrode section of said fluorescent tube, and adistance between said electrode section of said fluorescent tube andsaid reflector is smaller than a distance between said luminescencesection of said fluorescent tube and said reflector.
 9. The liquidcrystal display device as claimed in claim 7, wherein said electrodesection of said fluorescent tube is connected to a fluorescent tubesupport part having a heat conductivity equal to or greater than 0.5[W/(m·K)].
 10. The liquid crystal display device as claimed in claim 7,wherein said reflector is made of a metal or a material having a heatconductivity substantially equal to a heat conductivity of a metal.